In a pipe coupling used in a high-pressure fluid circuit, a seal ring and a backup ring that supports the seal ring are, generally, set between a male coupling member and a female coupling member to prevent leakage of a high-pressure fluid from therebetween in a state where the male coupling member has been inserted into and connected to the female coupling member (see Japanese Patent Application Publication No. 2005-42815).
There is a method of setting a seal ring and a backup ring wherein after the seal ring and the backup ring have been fitted in an annular groove formed on the outer peripheral surface of a male coupling member, the male coupling member is inserted into and connected to a female coupling member. This method suffers, however, from the following problem.
FIGS. 1 to 3 show an example of a way in which a male coupling member 1 is inserted into a female coupling member 2 in a conventional pipe coupling. The male coupling member 1 has an insert part 4 having substantially the same diameter as that of a male member reception hole 3 of the female coupling member 2. The insert part 4 has an annular groove 5 on the outer peripheral surface thereof. An elastic seal ring 6 and a backup ring 7 are set in the annular groove 5. The seal ring 6 is formed of a rubber or other material. The backup ring 7 is formed of a plastic or other material to have a relatively high rigidity. When the insert part 4 of the male coupling member 1 is inserted into the male member reception hole 3 of the female coupling member 2, the seal ring 6 is pressed between the inner wall surface of the male member reception hole 3 and the annular groove 5, causing the seal ring 6 to be elastically deformed to effect sealing.
The seal ring 6, however, is deformed by engagement with the end opening section of the male member reception hole 3 of the female coupling member 2 from the point of time when the insert part 4 of the male coupling member 1 begins to be inserted into the male member reception hole 3 of the female coupling member 2, and this causes the backup ring 7 to be pressed radially outward. The backup ring 7 is a split ring (i.e., a ring having a split, or cut, in a part thereof) to allow it to be inserted into the annular groove 5. Accordingly, if a radially outward pressure is applied to the backup ring 7 by the deformation of the seal ring 6, the backup ring 7 expands radially outward and may become outwardly dislodged from the annular groove 5 under certain circumstances before being inserted into the male member reception hole 3 (FIGS. 2 and 3).